Ablation planning system

ABSTRACT

An ablation planning system includes a user interface (104) configured to permit selection of inputs for planning an ablation procedure. The user interface is further configured to incorporate selection of ablation probes and one or more combinations of ablation powers, durations or parameters applicable to selected probes in the inputs to size the ablation volumes. The user interface includes a display for rendering internal images of a patient, the display permitting visualizations of the ablation volumes for different entry points on the internal images. An optimization engine (106) is coupled to the user interface to receive the inputs and is configured to output an optimized therapy plan which includes spatial ablation locations and temporal information for ablation so that collateral damage is reduced, coverage area is maximized and critical structures are avoided in a planned target volume.

This application is a continuation of U.S. application Ser No.14/235,140, filed Jan. 27, 2014, now U.S. Pat. No. ______ , which is anational stage entry of PCT/IB2012/053860 filed Jul. 27, 2012 (WO2013/014648), which claims priority to provisional application Ser. No.61/512,510, filed Jul. 28, 2011, provisional application Ser. No.61/514,914, filed Aug. 4, 2011, and provisional application serial no.61/566,630, filed Dec. 3, 2011, all incorporated herein by reference.

This disclosure relates to medical treatment systems and methods, andmore particularly to ablation planning systems and methods for patienttreatment with improved accuracy.

Microwave ablation (MWA) is a minimally invasive procedure used for thetreatment of localized tumors most commonly in the liver, kidney andlung. For large or irregularly shaped lesions, the treatment requiresmore than one session, and the physician has to plan in advance where toplace the needle and how many ablations are needed. MWA has become arecommended treatment modality for interventional cancer treatment, andhas received increasing attention in recent years. Compared withradiofrequency ablation (RFA), MWA provides more rapid and larger-volumetissue heating, and multiple antennae can be used simultaneously withsynergistic effects, e.g., the ablation volume may be increased beyondthat achievable with several sequential single-probe ablations. Inaddition, MWA is less susceptible to decreased ablation volumes due tothe heat sink effect (e.g., cooling provided by blood vessels adjacentto the tumor volume).

Mental planning of ablations is a daunting task. Physicians have topicture complete coverage of a three dimensional tumor volume usingoverlapping ellipsoidal ablation volumes in different orientations.Insufficient and imprecise planning leads to incomplete treatment andpotential recurrence of cancer or other effects. Conventionally, asingle ablation probe inserted through a single entry point is preferredto minimize trauma. However, if multiple probes are clinicallyavailable, large or irregularly shaped lesions could be treated moreeffectively than with conventional single probe units, thus potentiallydecreasing procedure time and complications. Mental planning can be aneven more daunting task with multiple entry points. Physicians have topicture and plan how to completely cover a three dimensional tumor usingan overlapping ellipsoidal ablation volume from different orientations.Insufficient and imprecise planning leads to incomplete treatment andpotential recurrence of cancer.

In accordance with the present principles, an ablation planning systemincludes a user interface configured to permit selection of inputs forplanning an ablation procedure. The user interface is further configuredto incorporate selection of ablation probes and one or more combinationsof ablation powers, durations or parameters applicable to selectedprobes in the inputs to size the ablation volumes. The user interfaceincludes a display for rendering internal images of a patient, thedisplay permitting visualizations of the ablation volumes for differententry points on the internal images. An optimization engine is coupledto the user interface to receive the inputs and is configured to outputan optimized therapy plan which includes spatial ablation locations andtemporal information for ablation so that collateral damage is reduced,coverage area is maximized and critical structures are avoided in aplanned target volume.

An ablation planning system includes a user interface configured topermit selection of inputs for planning an ablation procedure, the userinterface further being configured to incorporate ablation durations inthe inputs to size the ablation volumes. The user interface includes adisplay for rendering internal images of a patient. The display permitsvisualizations of the ablation volumes for different entry points on theinternal images, and the display is configured to render internal imagesof a patient and provide selection controls to enable a user to selectan internal image and a view of the internal image. A database isconfigured to store the internal images and information on the ablationprobes to assist in determining sizes and shapes for the ablationvolumes for a given planned target volume by associating power and timecharacteristics with the sizes and shapes of the ablation volumes. Anoptimization engine is coupled to the user interface to receive theinputs and is configured to output an optimized therapy plan whichincludes spatial ablation locations and temporal information forminimally needed ablation durations, so that collateral damage isreduced, coverage area is maximized and critical structures are avoidedin a planned target volume.

A method for planning an ablation procedure includes displaying aninternal image of a patient on a display of a user interface; selectingan ablation probe or set of probes for performing an ablation procedureusing the user interface; selecting a point or points of entry for theablation probe or set of probes on the internal image; inputtinginformation to an optimization engine for a set of inputs including theablation probe or set of probes selected, the point or points of entryselected, time and power information to determine sizes and shapes ofablation volumes; and outputting from the optimization engine anoptimized therapy plan based on reducing collateral damage, maximizingcoverage area and avoiding critical structures in a planned targetvolume.

These and other objects, features and advantages of the presentdisclosure will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

This disclosure will present in detail the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a block diagram showing a high-level embodiment of an ablationtherapy system in accordance with the present principles;

FIG. 2 is a diagram showing an illustrative graphical user interface forplanning an ablation procedure in accordance with one illustrativeembodiment;

FIG. 3 is another diagram showing the illustrative graphical userinterface of FIG. 2 showing image details for planning the ablationprocedure in accordance with the illustrative embodiment;

FIG. 4 is another diagram showing greater detail on an image forplanning the ablation procedure in accordance with the illustrativeembodiment;

FIG. 5 is a block/flow diagram showing steps for planning, executing ortraining for an ablation procedure in accordance with an illustrativeembodiment;

FIG. 6 is a block diagram showing a system for planning and performingan ablation procedure in accordance with the present principles; and

FIG. 7-I is a block/flow diagram showing steps for planning, executingor training for an ablation procedure using the system of FIG. 6 inaccordance with another illustrative embodiment.

FIG. 7-II is a block/flow diagram showing additional steps for planning,executing or training for an ablation procedure using the system of FIG.6 in accordance with another illustrative embodiment.

In accordance with the present principles, to generate a clinicallyrelevant and reliable result, an automated planning system is providedthat warrants precise locations of probes and complete coverage of tumorand margin (planned target volume, PTV). An automatic coverage method isdescribed. The searching for the best ablation centers is treated as aniterative non-linear optimization problem where a cost function isformulated as the weighted sum of un-ablated PTV volume and unwantedcollateral damage to the adjacent health tissue. This is a non-linearoptimization problem which aims to minimize cancerous tissue that isuntreated and the healthy tissue that is damaged. The entire planningsystem is implemented with a Graphic User Interface (GUI) that allowsfor interactive planning scenarios including proper probe selection,skin entry localization, ablation number specifications, etc. Theplanning system is integrated as a first step of an electro-magneticallyguided navigation system where planning is executed to permit plans tobe transferred to subsequent navigation working steps in an adaptivemanner.

Focal tumor ablation is an effective alternative to surgical resection.A microwave ablation (MWA) planning system in accordance with oneembodiment includes a database, an optimization engine and auser-interface. The system provides optimized ablation parameters asoutput to help physicians maximize tumor coverage, minimize collateraldamage to healthy tissue and/or optimize overall procedure execution inother ways, such as by avoiding critical structures, such as bloodvessels or the like. The system's user-interface componentadvantageously provides input/output specific to microwave ablation, butis also applicable to other ablation systems that have similarinformation needs (e.g., cryogenic ablation). Such a planning system canassist interventionists to best plan the ablation procedure usingresource information available from the database and informationspecified by the users as input. The output of the system includes butis not limited to the optimized ablation parameters computed by theoptimization engine.

To facilitate efficient and accurate execution of ablation procedures,ablation planning systems have addressed the needs for radio frequencyablation (RFA) procedures. Such planning systems generally determine thenumber and/or location of individual ablations that together allowcomplete and efficient eradication of a tumor. These planning systems,however, do not exploit the specific advantages of MWA technology whichmay include, e.g.: 1) The ability to customize an ablation size bychoosing specific power/time/temperature parameters when running the MWAdevice; and 2) The ability to insert several probes simultaneously withsynergistic effects, thus increasing the ablated volume further anddecreasing procedure time. As a result of the more rapid destruction oftissue, MWA procedures are generally more difficult to control than RFAand may cause harm if not used with care and confidence. A planningsystem in accordance with the present embodiments addresses MWA-specificparameters and workflows and is highly desirable to help physiciansachieve better microwave ablation results.

In contrast to RFA, MWA probes can produce ablations in a range ofablation sizes. The size of the ablation zone is a function of time andpower supplied to the probe. Planning systems geared towards RFA make norecommendation for specific power/time settings, nor are they able totake advantage of the variable ablation sizes in determining the optimalablation plan. Furthermore, there may be patient-specific considerations(or computational complexity and time constraints) that would limit thechoices of power/time settings that the physician is willing toconsider. There may also be patient-specific considerations or overalltime/throughput considerations that would make a particular treatmentapproach with multiple simultaneous probe insertions advantageous.

MWA manufacturers may provide only limited information on ablationvolume varied with power/time, and if provided, the ablation informationonly includes discrete power/time inputs and their correspondingablation sizes (e.g., ablation size at 5 minutes, 10 minutes, usingpower 50 W). It is difficult for users to extrapolate the size of anecrosis zone using discrete intervals of the given inputs (e.g.,ablation zone at 8 minutes). The present embodiments address theseshortcomings and clinical needs of the prior art by providing amicrowave ablation planning system with a user interface, optimizationengine, and other components that permit efficient planning andexecution of microwave ablation procedures.

It should be understood that the present invention will be described interms of microwave ablation; however, other ablation technologies arecontemplated. In particular, the present principles are particularlyuseful with ablation technologies that employ time dependent variationsfor ablation zones. In other embodiments, in addition to or instead oftime dependent ablation treatment volumes, other dependent variables maybe employed, such as, temperature-dependent variables, power-dependentvariables, etc.

It also should be understood that the present invention will bedescribed in terms of medical instruments; however, the teachings of thepresent invention are much broader and are applicable to any instrumentsemployed in treating or analyzing complex biological or mechanicalsystems. In particular, the present principles are applicable tointernal tracking and planning procedures of biological systems,procedures in all areas of the body such as the lungs, gastro-intestinaltract, excretory organs, blood vessels, etc. The elements depicted inthe FIGS. may be implemented in various combinations of hardware andsoftware and provide functions which may be combined in a single elementor multiple elements.

The functions of the various elements shown in the FIGS. can be providedthrough the use of dedicated hardware as well as hardware capable ofexecuting software in association with appropriate software. Whenprovided by a processor, the functions can be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which can be shared. Moreover, explicituse of the term “processor” or “controller” should not be construed torefer exclusively to hardware capable of executing software, and canimplicitly include, without limitation, digital signal processor (“DSP”)hardware, read-only memory (“ROM”) for storing software, random accessmemory (“RAM”), non-volatile storage, etc.

Moreover, all statements herein reciting principles, aspects, andembodiments of the invention, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture (i.e., any elements developed that perform the same function,regardless of structure). Thus, for example, it will be appreciated bythose skilled in the art that the block diagrams presented hereinrepresent conceptual views of illustrative system components and/orcircuitry embodying the principles of the invention. Similarly, it willbe appreciated that any flow charts, flow diagrams and the likerepresent various processes which may be substantially represented incomputer readable storage media and so executed by a computer orprocessor, whether or not such computer or processor is explicitlyshown.

Furthermore, embodiments of the present invention can take the form of acomputer program product accessible from a computer-usable orcomputer-readable storage medium providing program code for use by or inconnection with a computer or any instruction execution system. For thepurposes of this description, a computer-usable or computer readablestorage medium can be any apparatus that may include, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. Examples of a computer-readable medium include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Current examples of opticaldisks include compact disk—read only memory (CD-ROM), compactdisk—read/write (CD-R/W), DVD and Blu-ray™.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a high level block diagramshows a planning system 100 in accordance with one illustrativeembodiment. The planning system 100 assists doctors, technicians, etc.in generating a plan on how to ablate a tumor or other tissue, visualizethe ablation plan and evaluate quantitative metrics associated with theplan. A database or memory system 102 includes storage for informationon a set of ablation probes and their properties, e.g., power and/ortime data versus ablated volume, ablation shape/size characteristics,etc.

This information is made available to a user from the database 102 at auser-interface 104. It should be understood that an ablation probe canbe used interchangeably with ablation needle, ablation antenna, ablationapplicator, etc. An optimization engine 106 optimizes an ablation planand can read the probe properties of selected probes from the database102. The optimization engine 106 also considers user inputs, e.g.,selected probe, tumor segmentation, skin entry points, number ofablations, time/power preferences, etc. The optimization engine 106 usesthe inputs to create and communicate the ablation plan to theuser-interface for visualization and modification.

In one embodiment, the planning system 100 includes a microwave ablation(MWA) planning system. The system 100 addresses MWA-specific parameters(variable ablation sizes as a function of power, time and temperature)and workflows that help physicians achieve better microwave ablationresults.

The ablation probe database 102 includes all relevant properties fordifferent ablation probes, for example, size of the ablation zone as afunction of different times, power settings for a given probe, etc. Thedatabase 102 provides resource information of ablation probes and alsoallows users to refine the probe properties through the user interface104. The user interface 104 permits user input and selection of allparameters relevant for optimizing the ablation plan, and display (andselect) results and choices that become the output of the plancomputation. The inputs may include, e.g., tumor segmentation, one ormore skin entry points, number of ablations either in total or by numberof ablations from each entry point, selection of one or more ablationprobes applicable to all entry points or to specific entry point(s), asubset of power/time settings to be considered for a given ablationprobe, etc. The displayed plan outputs may include, e.g., number andlocation of ablations, shape/sizes and power/time settings of eachablation, etc. User choices based on plan output may include, e.g.,choosing one of several possible power/time settings to achieve theplanned shape/size of a given ablation.

The optimization engine 106 optimizes a treatment plan and may beemployed to monitor activities to make suggestions for future actionsbased upon the execution of previous events. The user-interface 104interacts with the ablation probe database 102 and passes parameters tothe optimization engine 106. The parameters include, for example, auser-specified set of ablation probes and a user-specified set ofpower-time characteristics to be used with those ablation probes. Theoptimization engine 106 computes an ablation plan based on the inputsfrom the user interface 104, and the resource information from theablation pro database 102. The optimization engine 106 passes theablation plan results back to the user interface 104 for display and,optionally, additional user choices as input. The ablation plan may betailored to achieve a number of objectives, e.g., maximize tumorcoverage, minimize number of ablations, minimize time of ablations,minimize collateral damage, etc. The optimization engine 106 is howevernot restricted to these objectives.

In one embodiment, a search for the best ablation coverage can be seenas an iterative optimization problem. The ablation centers are steeredtoward the location which minimizes both un-ablated planned targetvolume (PTV) (tumor tissue that ought to be ablated but is not yetablated) and collateral damage caused to healthy tissue. Theoptimization problem can thus be presented as:

$\begin{matrix}{\hat{\Theta} = {\arg {\min\limits_{\Theta}{C\left( {V_{PTV},{\sum\limits_{i}{V_{Ai}\left( {\Theta_{i},e_{i}} \right)}}} \right)}}}} & (1)\end{matrix}$

where V_(PTV) is the planned target volume (PTV) and V_(Ai) is thei^(th) ablation volume characterized by the parameter set Θ_(i) at givenskin entry point e_(i). C is the cost function. Θ_(i) is a fourdimensional (4D) parameter defined as:

Θ_(i)=[t_(x)t_(y)t_(z)s ]^(T)   (2).

The ablation center (the center of the ellipsoidal ablation model) isdenoted as t_(x), t_(y), t_(z)in three dimensions. s is a scale factorbetween 0 and 1 that parameterizes the radii from minimum to maximum.

Unlike RF ablation where the power and time are fixed and the ablationsize is invariant, microwave ablation manufacturers may provide an arrayof ablation sizes and their respective power/time settings. A model inaccordance with the present principles interpolates microwave ablationradii from available discrete power/time inputs, assuming radii growproportionally with increasing time and increasing power. Otherrelationships are also contemplated.

An iterative search problem may be implemented using, e.g., optimizationtechniques to minimize the following illustrative cost function C:

C=V_(PTV)∩(∩V_(Ai) )·μ_(u)+V_(PTV) ∩(∪V_(Ai))·μ_(c)+φ·μ_(p)   (3)

where V_(PTV) is the PTV volume, V_(Ai) is the i^(th) ablation volume,μ_(u) and μ_(c) are the weighting factors for unablated PTV andcollateral damage, respectively. The symbol ∩ between two volumesrepresents the count of voxels that are set in both volumes(intersection of the two volumes), whereas the symbol U∪ represents thecount of voxels that are set in either volume (union of the twovolumes). The horizontal bar above the two volumes, V_(PTV) and theunion of all the ablation volumes ∪V_(Ai) in the cost functionexpression, represent the inverse of the volumes, i.e., voxels that are“excluded” from the respective volumes. The cost function is normalizedbased on these weights which reflect user preferences in penalizingunwanted results.

In case of some undesirable situations, a penalty function φ will beintroduced. For example, for simultaneous ablation, a requirement may beprovided that adjacent ablations performed simultaneously are to be kepta minimum distance apart to ensure that the ablation process isperformed optimally. The penalty function φ is then defined as afunction of the distance between adjacent ablation centers. We add apenalty to the cost function using the third expression μ_(p)·φ toensure the adjacent needle ablation centers are not too close. Anotherexample of a penalty function is when a critical structure is presentclose to the PTV. The method may penalize the situation where theablation volume overlaps with the critical structure. The method willsuccessively iterate until convergence, and an optimum solution for Eq.(1) is achieved. During this process, the V_(PTV) (PTV volume) isconstant, V_(Ai) (ith ablation volume) is changed with positive ornegative perturbations of four independent parameters from set Θ_(i).The probe is permitted to be repositioned after the first session forsequential ablation sessions. For single-entry ablation, the probe isallowed to move anywhere within the PTV (unconstrained search); whilefor multi-entry ablation, the probe is allowed to move along thetrajectory between entry point and ablation center (constrainttrajectory search). For example, in sequential multi-ablation sessions,the probe can be repositioned after each ablation in an unconstrainedway. When using multiple skin entry points for simultaneous ablations,the probes are only allowed to move along the trajectory between entrypoint and ablation center (constraint trajectory search), in accordancewith how ablations are executed in clinical practice.

For modeling synergetic effects using simultaneous MWA applicators, thecost function C could be adjusted such that when the needles are mostlyparallel, the synergetic ablation volume which is supposed to be largerthan the summation of individual ablations could be extrapolated fromthe manufacturer's data brochure. The optimization engine 106 considersthe objectives that provide parallel needles to create a larger ablationzone. In another embodiment, ablation sizes could be modeled usingprincipals of thermal physics including, e.g., tissue properties,thermal coefficients will be integrated into the model and employed toestimate ablation regions using power and time data.

Referring to FIG. 2, a planning tool or ablation treatment planningsystem 200 includes a graphical user interface of the user-interface 104for therapy planning. The ablation treatment planning system andcoverage algorithm 200 provide image manipulation of pre-operative CTimages 220. Quick 3D automatic or semi-automatic (involving some userinteraction) segmentation of tumors can be performed, and once a tumoris segmented, a margin which typically ranges from 5-10 mm can beconveniently added to decide the planned target volume (PTV). The useris then asked to pick the preferred ablation needle and one or morepreferred needle entry points on the patient's skin. Based onmanufacturers' data brochures and published literature on animal/patienttrials using these probes, an ablation template can be modeled as eithera spherical or ellipsoidal three dimensional object with three knownradii. The method can be easily extended to other geometrical shapes ifnecessary.

In one embodiment, the system 100 prompts users to select an ablationprobe from an ablation probe menu or pane 202 and specify a preferredpower and time combination(s) to be considered for the given ablationprobe in an applicator properties sub-screen 230 that pops up when theprobe or applicator is selected in the pane 202. The sub-screen 230 mayinclude a power/time table 232 listing in a matrix of powers and timesand their resulting ablated volume. For each power/time setting, thetable 232 provides information about a size of the ablation volumemodeled as an ellipsoid-shape 3D structure with three distinctive radiiin three dimensions (e.g., Ellips (2,3,0.5). Other shapes may also beemployed. The user may select the modeled shape that is desired andapply the shape at a particular location in an image screen 225. Theseuser inputs may be based on user experience and understanding of thepatients' anatomy, and help to confine the search space for theoptimization engine 106.

The tool 200 may be employed to chart out or plan a complete procedure,selecting different probes, different shapes, different power/times,etc. The planning tool 200 may include user-selected functions to permitplanning using different technology, e.g., by selecting one of fields204 (RFA or MWA). Other technologies may be added as well. Suchtechnologies would include at least time/power dependent ablation volumeshapes to provide a highly customizable and flexible ablation plan. Theuser may select different patients 208, different scans 210, differentviews 212, etc. from a memory or database storing these items. Adescription pane 206 may be provided, which includes data on the images,views, patients, etc. Other useful functions 214 may also be provided,such as export a plan, print, report, zoom, etc.

Referring to FIG. 3, a user-interface instance 300 of the microwaveablation planning system 200 is illustratively shown in accordance withone embodiment. The instance 300 illustratively includes an image 302,e.g., a computed tomography scan, magnetic resonance image, etc. In thisexample, the image 302 includes a section 306 of a liver with asegmented tumor 308. Skin entry points 310, 311 are specified by theuser. For each skin entry point 310, 311, an ablation probe is selectedwith preferred power/time settings from the menu/table 232 in pane 230.The optimization engine 106 provides an ablation plan that includesplanned ablation volumes 312 with the recommended microwave ablationtime and power settings based on pre-defined optimization objectives.The skin entry points 311 are for parallel needles, which may beemployed to reduce overall ablation time, as one alternative.

Using the selected entry point(s) 310 or 311 on the skin, a singleellipsoidal ablation is overlaid on the PTV to aid in understanding thesize of an ablation. It would be difficult for a radiologist to arriveat an estimate for the number of ablations needed to cover this complex,highly irregular-shaped PTV with the given ablation shape. The presentembodiments compute solutions based on different entry points and resultin overlapping spherical/ellipsoidal ablations that optimally cover thePTV with minimal collateral damage. With the aid of visualization, theradiologist can determine if the number of ablations and the collateraldamage are acceptable. Since the computation is quick, it is easy tomodify the entry point or needle to create an alternative plan. Also,the estimation of tumor coverage is done in a fully automatic fashion.

Referring to FIG. 4, an image 400 is illustratively shown to demonstratesome of the features in accordance with the present principles. Image400 includes a scan section having an irregularly shaped tumor 410.Entry point-1 404 is shown for providing a planned ablation volume 408,and entry point-2 402 is shown for providing a planned ablation volume406. The highly irregular tumor 410 is covered by a PTV which includestwo ablations (406 and 408) using a Covidian-Evidence™ MWA probe at 45W. An estimated percentage of PTV coverage is 99.86% with 11.13 cm³ ofcollateral damage in this case. As the output of the algorithm, ablation408 from the entry point-1 404 is suggested to ablate for 5.3 minutes,whereas the ablation 408 from entry point-2 402 is suggested to ablatefor 9.3 minutes.

Referring again to FIG. 1 with continued reference to FIGS. 2-4, thesystem 100 prompts the user to provide the preferred power/time settingfor the selected probes and user-selected entry points. The optimizationengine 106 provides an ablation plan with a list of power and timecombinations that could be employed for the selected ablation probe(s),to satisfy pre-defined optimization objectives, e.g., maximize tumorcoverage, minimize number of ablations, minimize time of ablations,minimize collateral damage, etc. The optimization engine 106 may alsoconsider alternative entry points, ablation times, probes, etc. tobetter achieve these objectives.

The planning system's input can take a variety of forms in terms ofcomponents to be visualized and presentation style. For example, userinput could include one or more of these components: tumor segmentation,one or more skin entry points, number of ablations either in total or bynumber of ablations from each entry point, selection of one or moreablation probes, a subset of power/time settings to be considered for agiven ablation probe, inter-probe distance (applicable to parallel probeinsertions), etc. The user input could be presented in one of multiplegraphical user interface forms e.g.: table, checklist, spreadsheet,drop-down menu, information window which provides drawing and annotationof ablation zone in 2D or 3D for a given ablation setting, etc. Theselection of one or more ablation probes may be performed manually orautomatically. For example, ablation probe types could be manuallyspecified by user-input, or they could be pre-selected in theuser-interface via an automatic detection of probes connected to thesystem.

The planning system's output can also take a variety of forms in termsof components to be visualized and presentation style. The planningsystem's output may include one or more of a recommended power and timefor any selected probe, shape/sizes of each ablation, recommended entrypoint locations, recommended probe types, a recommended number ofablations to be considered for each skin entry point, etc. The planningsystem's output could be presented in one of multiple graphical userinterface forms, such as, e.g., a table, a highlighted list, a markedspreadsheet, a display and/or an overlay of estimated ablationzone/parameters onto the original images (e.g., CT) with power/timesuggestions, metrics of tumor coverage (percentage of tumor coverage,collateral damage), etc.

In one embodiment, outputs (e.g., power and time for a given probe) canbe a subset of the input selections. Output of the system may alsoinclude error/warning messages. The system could flag a warning message,indicating the user selection is not appropriate given the patientanatomy and the tumor size/geometry, etc. In one example, the selectedpower and time settings may not be able to cover the entirety of thetumor. If necessary, the user can choose to override the recommendedsettings by discarding the current plan and running a new instance ofthe plan using new combinations of inputs. Where the planning system 100provides an output that includes recommended ablation probe types andpower/time settings for the recommended probes, the system 100 may alsobe used for other parameter optimization. For example, in oneembodiment, if the users have only a small selection of ablation probes,the system could specify which probe should be chosen to treat thisspecific patient, as a result of the estimation from optimization engine106. In another embodiment, the system 100 could specify which skinentry points are beneficial for use in the procedure based on theobjectives included in the optimization engine 106.

Preferred embodiments are applied to image-guided microwave ablation;however, other ablation systems may be employed, especially where thereis high dimensional parameter space for each insertion and ablation. Forexample, for other ablation modalities (e.g., HIFU, Cryo) where variableablation sizes also vary with specific input parameters, theseparameters can be specified by the users as the input for the planningsystem 100, and optimized through the optimization engine 106, resultingin the output for optimized parameters. Unlike RF ablation where thepower and time is fixed and the ablation size is invariant, microwaveablation provides an array of time and power settings, and can vary intheir respective ablation sizes as needed. For a given power, a modelcan interpolate microwave ablation radii from a shorest time to alongest time, assuming three radii grow proportionally with time. Inthis way, ablation shapes and sizes may be determined and implementedusing a specific time and power combination. Given the size and shapeneeded for an ablation can be provided by applying an appropriate timeof ablation.

To assess the accuracy of the planning methods disclosed, the presentinventors created, on pre-operative CT images, a series of lesions withknown geometries, i.e., spherical and ellipsoidal PTVs are synthesizedto serve as the ground truth. Estimated ablation centers, if plannedproperly, should coincide with the center of the geometry of thesespheres/ellipsoids. In addition, the estimated ablation radii shouldcircumscribe the boundary of the PTV with minimal damage to the healthytissue. Among thirty runs on three known geometry centers (one sphere,two ellipsoids), the Mean Location Distance Error (MLDE) which isobtained by comparing the computed ablation center with the ground truthablation center achieves 0.66 mm (STD: 0.22 mm). The Mean Radii DistanceError (MRDE) which is estimated by comparing the computed ablation radiiwith the ground truth radii reaches 0.53 mm (STD: 0.23 mm). Thesepreliminary and illustrative results demonstrate the accuracy androbustness of the described embodiments. Table 1 shows comparisonresults for the simulations to demonstrate the accuracy and feasibilityof the disclosed methods.

TABLE 1 MLDE (mm) and MRDE (mm) are estimated based on the comparisonwith the ground truth after ten runs of the optimization algorithm.Three known geometries on two PTVs are used for this testing. MLDE_xMLDE_y MLDE_z MLDE MRDE_r (mm) (mm) (mm) (mm) (mm) PTV1: one 0.71 ± 0.430.41 ± 0.07 0.87 ± 0.07 0.66 ± 0.14 0.21 ± 0.07 ablation PTV2: 1st 1.06± 0.59 1.42 ± 0.83 0.34 ± 0.25 0.94 ± 0.44 0.99 ± 0.54 ablation PTV2:2nd 0.76 ± 0.13 0.11 ± 0.09 0.24 ± 0.16 0.38 ± 0.07 0.41 ± 0.08 ablationMean 0.85 ± 0.38 0.65 ± 0.33 0.48 ± 0.16 0.66 ± 0.22 0.53 ± 0.23

Referring to FIG. 5, a method for planning an ablation procedure isdepicted in accordance with illustrative embodiments. In block 502, aninternal image of a patient on a display of a user interface may bedisplayed. The image may be a pre-operative image, a rendering of animage or a model employed for simulation or practice. The image may be a2D image or a 3D image and may include multiple views that can becontrolled using the user interface. In block 504, an ablation probe orset of probes for performing an ablation procedure using the userinterface is/are selected. The ablation probe may include a microwaveablation probe, and the information preferably includes power and timedata for a plurality of ablation shapes. The shapes may includespherical or ellipsoidal shapes, although other shapes may be employedas well. In block 506, a point or points of entry for the ablation probeor set of probes is/are selected on the internal image. Other inputinformation may also be selected or provided by a user. In this way, theexperience of the user and the convenience and power of a computersystem can be combined to provide a synergistic and powerful planningtool. In block 508, information about the ablation probe or set ofprobes and the point or points of entry are input to an optimizationengine. Time and power is included in the input information to determinesizes and shapes of ablation volumes. The time and power are providedfor time dependent ablation volumes, e.g., the ablation volume isproportional to the time/ablation duration. Other information may alsobe included in the input. In block 509, the set of inputs may includeone or more of a type of ablation probe, a margin of error, ablationcoverage, collateral damage, ablation time, etc.

In block 510, an optimized therapy plan is output from an optimizationengine based on, e.g., reducing collateral damage and maximizingcoverage area in a planned target volume. Other criteria may be set aswell instead of and/or in addition to the damage and coverage criteria.In block 512, the optimization of the therapy plan may includeminimizing a cost based on a set of inputs. The inputs may include atleast the point or points of entry and the information on the ablationprobe or set of probes. In block 514, cost minimization may includecomputing a penalty function to penalize the cost for an unwantedeffect. The penalty function may be tailored to account form one or moreeffects, such as employing multiple probes, ablation sites that are tooclose, anatomical features that are nearby, etc. The cost function andpenalty function may be altered in real-time at the user interface byselecting different scenarios or physiological conditions in a patient,e.g., entering blood flow conditions for a nearby blood vessel,accounting for scar tissue, entering physical properties measured for aspecific patient, etc. The optimized therapy plan may include one ormore types of ablation probes, locations of entry points, a number ofablation probes used, locations for a minimum number of ablations,ablation locations to minimize collateral damage, a minimized ablationtime, etc. In block 518, the recommendations and/or outputs may beautomatically input to a navigation system to carry out the therapyplan. In block 520, the system may be employed in providing an interfacefor carrying out an ablation therapy procedure (or providing training).

Referring to FIG. 6, a treatment system 600 for ablation therapy isshown in accordance with one illustrative embodiment. System 600 may bepart of a therapy planning and procedure monitoring workstation 601 thatlinks optimized plan information, tissue interaction modeling, dosemonitoring, and clinical outcomes data based on a patient-specific basisfor procedure optimization, reporting, and physician training. System600 may include memory storage 604. The database 604 stores images 611,preferably three-dimensional (3D) images, of a patient 622 on which aprocedure is to be performed. Workstation 601 includes a processor 606capable of execution of an optimized therapy plan 607 stored in memory604.

An ablation probe navigation system 608 is preferably controlled by andprovides data to the computer 606. The procedure may be conductedmanually as well, without the navigation system 608. The navigationsystem 608 receives spatial information, commands from the workstation601 and carries out the plan 607 created by the planning system 100. Theworkstation 601 and the planning system 100 may be integrated togetheror may be separate units.

An ablation probe or a set of probes 630 are selected and coupled to thesystem 600. In one embodiment, the database 102 and optimization engine106 are stored in memory 604. The probe information may be referencedfrom the memory 604 to obtain the information needed for planning thetherapy. In another embodiment, by connecting the probe or probes 630 tothe system 600, the system senses the types of probes and looks up theprobe data from memory 604. Feedback from the ablations on a target 632in accordance with the plan 607 may be collected by sensors or by animaging system 610, which may include fluoroscopy, ultrasound, etc. Thefeedback may include PTV coverage area, measured temperatures, etc.Programming, device control, monitoring of functions and/or any otherinteractions with the workstation 601 may be performed using the userinterface 104. A display 619 may also permit a user to interact with theworkstation 601 and its components and functions, or any other elementwithin the system 600. This is further facilitated by the interface 104which may include a keyboard, mouse, a joystick, a haptic device, or anyother peripheral or control to permit user feedback from and interactionwith the workstation 601 or system 600.

Referring to FIG. 7-1, a block/flow diagram shows workflow 700 for thesystem 600 in accordance with one illustrative embodiment. In block 702,inputs for a therapy plan are illustratively described. In block 704, adisplay of 2D and/or 3D images of a target anatomy in one or more viewsis provided on the display (619) of the graphical use interface (104).In block 706, treatment volume related inputs are provided. Examples oftreatment related inputs include, e.g., an outline of a planned targetvolume with margins for treatment coverage inclusion as provided inblock 708. In block 710, critical structures are outlined for coverageexclusion (e.g., tissues that should not be damaged by ablation). Inblock 712, another input type includes ablation probe related inputs.These inputs or at least default inputs can be obtained from a database.In block 714, an ablation probe or probes are selected for treatment. Inblock 716, ablation power/time characteristics of selected probes areset. The power/time information is based on the probe selection and isemployed to derive a size and shape of the ablation regions. In otherwords, an ablation region of a particular size and shape may be selectedbased upon time/power characteristics. The sizes and shapes arecompletely customizable based upon temporal data for a given power.

Another input type may include entry point data in block 718. In block720 one or more entry points for the ablation probe or probes areselected on the image. In block 722, selected ablation probes areassociated with the entry point or points. Different entry points andassociated probe types may provide different results. So thesecombinations may be provided as a form of input. In block 724, a desirednumber of ablations are also associated with each entry point. In block726, criteria, weightings, margins of error, penalties, etc. are alsoinput for therapy planning optimization.

FIG. 7-II is a block/flow diagram showing additional steps for planning,executing or training for an ablation procedure using the system of FIG.6 in accordance with another illustrative embodiment. In block 728, anoptimization engine provides an optimized therapy plan based upon theinputs provided from block 702. An optimized therapy plan is computed inblock 730. In block 732, a cost function or functions are employed onthe inputs to optimize the plan. In block 734, the optimization engineadapts all inputs (e.g., ablation locations, sizes, shapes, power, time,inclusion regions, exclusion regions, etc.) to reach an optimal costfunction value as the plan result.

In block 736, a therapy plan result is output and visualized. The outputmay include types and number of ablation probes, locations of entrypoints, locations for ablation centers, minimum number of ablationsneeded, minimum ablation time needed, predicted ablation metrics,collateral damage, unablated planned target volume regions, and damageto critical structures. In block 738, planned ablation volumes for eachablation are visualized on the display. In block 740, untreated tumorvolume is also visualized on the display. In block 742, planned ablationprobe trajectories are visualized for each entry point and ablation. Inblock 744, power, times, ablation size and shape, etc. are visualizedfor each ablation. In block 746, quantitative coverage metrics arecomputed (e.g., PTV coverage, etc.). In accordance with the results inblock 736, a check is made in block 748 to determine if the therapy planis acceptable. Acceptability may be based on any number of criteria,e.g., coverage, minimum number of ablations, time of procedure, etc. Ifunacceptable, the flow path returns to block 702 and calls for anadjustment or modification of the inputs. Replanning is performed toachieve updated results based on the new inputs.

In interpreting the appended claims, it should be understood that:

-   -   a) the word “comprising” does not exclude the presence of other        elements or acts than those listed in a given claim;    -   b) the word “a” or “an” preceding an element does not exclude        the presence of a plurality of such elements;    -   c) any reference signs in the claims do not limit their scope;    -   d) several “means” may be represented by the same item or        hardware or software implemented structure or function; and    -   e) no specific sequence of acts is intended to be required        unless specifically indicated.

Having described preferred embodiments for an ablation planning system(which are intended to be illustrative and not limiting), it is notedthat modifications and variations can be made by persons skilled in theart in light of the above teachings. It is therefore to be understoodthat changes may be made in the particular embodiments of the disclosuredisclosed which are within the scope of the embodiments disclosed hereinas outlined by the appended claims. Having thus described the detailsand particularity required by the patent laws, what is claimed anddesired protected by Letters Patent is set forth in the appended claims.

1. A microwave ablation planning system, comprising: a user interfaceconfigured to permit selection of inputs for planning an ablationprocedure using multiple ablation probes, the user interface furtherconfigured to enable a user to select the multiple ablation probes forthe ablation procedure, a location of a skin entry point for each of theselected multiple ablation probes, and one or more combinations ofablation powers, durations, or parameters applicable to the selectedmultiple ablation probes, wherein the selected inputs determine sizesand shapes of ablation volumes, wherein the user interface furtherincludes a display configured to render internal images of a patient,wherein the display is further configured to display visualizations ofthe ablation volumes on the internal images; a database configured tostore information related to the multiple ablation probes such that theinformation is retrievable by the user interface to select the multipleablation probes to be employed as the inputs, wherein the multipleablation probes are microwave ablation probes and wherein the storedinformation includes power and duration information corresponding to aplurality of ablation volume sizes and shapes; and an optimizationengine coupled to the user interface and configured to receive theinputs and configured to output an optimized microwave ablation therapyplan which includes spatial ablation locations and power and durationinformation such that in a planned microwave ablation target volumecollateral damage is reduced, ablation coverage is maximized, andcritical structures are avoided.
 2. The system as recited in claim 1,wherein the optimization engine computes a cost based on the inputs andminimizes the cost to determine the output optimized microwave ablationtherapy plan.
 3. The system as recited in claim 2, wherein theoptimization engine includes a penalty function to penalize the cost forunwanted effects.
 4. The system as recited in claim 1, wherein theinputs include one or more of the planned target volume to be covered inthe microwave ablation therapy plan, a margin of error, ablationcoverage, collateral damage, regions to be excluded, ablation power, andablation duration.
 5. The system as recited in claim 1, wherein theoutput includes locations for ablation centers, a minimum number ofablations, a minimum ablation power or duration, predicted ablationmetrics, collateral damage, unablated planned target volume regions, anddamage to critical structures.
 6. The system as recited in claim 7,wherein the plurality of ablation shapes include ellipses, a major axisof each ellipse lying along a trajectory between an ablation volumecenter and a corresponding skin entry point, radii of each ellipse beingcontrolled by the ablation power and duration.
 7. The system as recitedin claim 1, wherein the optimization engine is configured to interpolatemicrowave ablation radii from the power and time data for a plurality ofablation shapes by assuming the ablation radii grow proportionally withincreasing ablation duration and increasing ablation power.
 8. A methodfor planning a microwave ablation procedure, comprising: displaying aninternal image of a patient on a display of a user interface, whereinthe user interface is configured to permit selection of inputs forplanning an ablation procedure using multiple ablation probes, the userinterface further configured to input a selection of the multipleablation probes, input a location of a skin entry point for each of theselected multiple ablation probes, and input one or more combinations ofablation power and duration for the selected ablation probes to sizeablation volumes, the user interface including a display configured torender internal images of a patient and visualize the ablation volumes,and the skin entry points on the internal images; wherein the multipleablation probes are microwave ablation probes, a size of the ablationvolume of each of the microwave ablation probes being controlled byapplication power and duration supplied to each microwave ablationprobe; selecting a plurality of the ablation probes for performing theablation procedure using the user interface; selecting a location of theskin entry point for each of the multiple ablation probes on theinternal image; generating an optimized microwave ablation plan whichincludes spatial ablation locations and ablation power and durationinformation that reduces collateral damage, maximizes ablation coveragearea, and avoids critical structures in a planned target volume; andoutputting the optimized therapy plan.
 9. The method as recited in claim8, wherein generating the optimized microwave plan includes minimizing acost based on the selected inputs.
 10. The method as recited in claim 9,further including computing a penalty function to penalize the cost foran unwanted effect.
 11. The method as recited in claim 9, wherein theselected inputs includes one or more of a margin of error, ablationcoverage, collateral damage, regions to be excluded, the ablation power,and the ablation duration.
 12. The method as recited in claim 8, whereinthe optimized microwave ablation plan includes locations for ablationcenters, a minimum number of ablations, a minimum ablation power orduration, ablation metrics, collateral damage, unablated planned targetvolume regions, and damage to critical structures.
 13. The method asrecited in claim 8, wherein optimizing the microwave ablation planincludes interpolating microwave ablation radii from the power andduration for a plurality of ablation shapes and/or sizes by assuming theablation radii grow proportionally with increasing duration andincreasing power.
 14. The method as recited in claim 8, wherein at leastone of the microwave ablation probes is configured to generate anellipsoidal ablation volume, radii of the ellipsoidal ablation volumebeing proportional to the ablation power and duration, a major axis ofthe ellipsoidal ablation volume being defined by a trajectory betweenthe ablation volume and the corresponding skin entry point, and whereinoptimizing the therapy plan includes adjusting the ablation power andduration and the skin entry points.
 15. A microwave ablation planningsystem for planning ablations of targets with complex shapes comprising:a display configured to render internal images of an internal region ofa patient including tissue to be ablated, the display further beingconfigured to visualize a planned target ablation volume to be ablated,ablation volumes of each of a plurality of microwave ablation probes andskin entry points, each skin entry point defining a trajectory from theskin entry point to an ablation center to a corresponding one of theablation volumes; a user interface configured to enable selection of atleast two of the plurality of microwave ablation probes and to retrievean ablation duration and power to ablation volume shape relationship forthe selected microwave ablation probes; one or more processorsconfigured to: determine a microwave ablation plan which maximizescoverage of the planned target volume and avoids critical structures,the microwave ablation plan including identifiers of the selected atleast two of the microwave ablation probes, an entry point correspondingto each identified microwave ablation probe, power applied to eachidentified microwave ablation probe, and a duration the power is appliedto each identified microwave ablation probe.
 16. The system as recitedin claim 15, wherein the one or more processors are further configuredto control the display to render the internal images of the internalregion of the patient, visualize the planned treatment volume, andvisualize the volume ablated by the two or more selected microwaveablation probes pursuant to the microwave ablation plan.
 17. The systemas recited in claim 16, wherein the user interface is configured toallow a clinician to adjust the entry points, the ablation powers, andthe ablation durations.
 18. The system as recited in claim 15, whereinthe one or more processors is configured to determine the microwaveablation plan using a cost function.
 19. The system as recited in claim18, wherein determining the microwave ablation plan further includesusing a penalty function.